Motor fuel



Moron FUEL Thomas H. Risk, Moorestown, N. 3., assignor to Ethyl Corporation, New York, N. Y., a corporation of Delaware N Drawing. Application September 8, 1954, Serial No. 454,854

1 Claim. (Cl. 4457) This invention relates to an improved fuel for use in glow-plug engines, particularly engines used to power model airplanes and model automobiles.

The current trend in the design of model motors-used to power model planes and racing cars is toward the glow-plug design. This is a two-cycle engine which employs an electrically heated glow-plug for starting only. The inlet and exhaust valves are cylinder ports uncovered by the piston near the bottom of its stroke. The saving in weight realized by the elimination of the ignition system and its accessories give this type of motor a material advantage in powering model planes. The simplicity of the design of these motors permits them to be made largely from die castings which reduces their cost to a low figure.

However, full advantage of this type of motor has not been realized because of the lack of a proper fuel. It is necessary that the fuel for these engines serve both as a fuel and as a lubricant. Thus, fuels for these motors contain 10 to 30 per cent of a relatively heavy lubricating oil, usually castor oil. The use of the lubricating oil does, however, present a problem in that it is difficult to obtain a fuel which starts easily and which does not cause the engin to seize at high speeds. Heretofore the usual commercial fuels are composed of various constituents such as nitromethane, alcohol, diethyl ether, and occasionally some hydrocarbon mixtures. These fuel mixtures are not satisfactory due to the fact that they are unstable in storage and in use frequently caused the engine to seize. Furthermore, the previously used fuels did not have a high enough heat content to give long runs in the engine which are essential for model planes and racing cars.

I have found that a fuel for this purpose must have the following properties: (1) ease of starting, (2) high power output, (3) resistance to seizing, (4) burning cleanliness, and (5) storage stability. It is, therefore, among the objects of my invention to provide a fuel having these properties.

I have found that a fuel containing an alkyl mononitrate ester containing from 3 to 5 carbon atoms, a heavy lubricating oil, and a paraflinic gasoline of medium antiknock properties accomplishes the above object. In addition, while not absolutely essential, the presence of an additional ingredient to aid in the prevention of seizing is quite helpful.

The alkyl mononitrate esters containing from 3 to 5 carbon atoms in the molecule which can be used in the fuels of this invention are n-propyl nitrate, isopropyl nitrate, n-butyl nitrate, isobutyl nitrate, sec-butyl nitrate,

tert-butyl nitrate, any of the eight isomeric forms of amylor pentyl nitrate, or mixtures of the isomeric forms of such mononitrate esters. These mononitrate esters should be used in amount between and 80 per cent by volume of the total fuel, and preferably between 20 and 40 per cent. Amounts lower than 10 per cent are relatively ineffective.

The above alkyl mononitrate esters containing from 3 2,764,477 Patented Sept. 25, 1956 "ice to 5 carbon atoms have been found to be excellent ignition starters for glow-plug engines. Moreover, these esters possess an oxygen balance such that during combustion, my fuel compositions have no tendency of explosive decomposition. That is, a feature of my fuels is that I have found that the percentage of nitrate radical with respect to total weight of the nitrate ester is an important factor in contributing to the over-all superior performance characteristics which th compositions of this invention exhibit. Thus, attempts to use alkyl nitrates having a higher percentage of nitrate radical in the molecule results in decomposition of an explosive nature in :an operating glow-plug engine. For example, methyland ethyl nitrates, while bearing a superficial resemblance to the mononitrate esters I employ, are unsatisfactory in accomplishing my objectives. Since glow-plug engines are built from light weight materials and are thus relatively fragile, attempts to use methylor ethyl nitrates in my fuel compositions result in unusually high wear problems and other operational difficulties arising by virtue of the overly powerful fuel detonation which such nitrate esters produce. Another characteristic of the mononitrate esters I employ making them eminently suitable for my purposes is their ideal flash points. If the flash point is too low, there is a serious fire hazard, especially if spillage of fuel occurs when refueling an engine which has been warmed up. On the other hand, if the flash point of the ester is too high, serious difficulty in starting such engines is the result.

A relatively heavy lubricating oil should be used having an SAE viscosity of more than 40. Such lubricating oils which can be used are castor oil, naphthenic oils, parafiinic oils, Pennsylvania bright stock, and the like. The amount of hydrocarbon lubricating oil should be between 10 and 40 per cent and preferably should be in the range between 15 and 30 per cent.

The gasoline constituent of my fuel must be substantially paraffinic. In other words, I have found that while the gasoline constituent can be a blend of gasoline hydrocarbons, such a blend must contain a substantial proportion of hydrocarbons of a paraflinic nature. For optimum results I prefer p arafiinic gasolines containing at least about 50 per cent by volume of paraflinic hydrocarbons. The octane number of the gasoline constituents of my fuels is important-the octane number should not be too low or else destructive detonation will result, and it should not be too high or else difiiculty in starting will occur. Thus, aromatic hydrocarbons, such as benzene, are deleterious unless present in minor proportions in a substantially paraflinic gasoline blend having the proper octane number. Preferably, the octane number should be in the range of about 40 to 60. The amount of such gasoline used should be in the range of 10 to per cent by volume, and preferably up to 40 per cent should be used and generally not more than about 60 per cent.

Ingredients to aid in the prevention of seizing are oleic acid, stearic acid, palmitic acid, glycerol, polyethylene glycol, naphthenic acid, naphthoic acid, lauric acid, and myristic acid. The amount of this ingredient should be between 1 land 10 per cent by volume and preferably between the range of 2 and 5 per cent.

To show the superiority of my fuel over those presently used, a mixture, by volume, of 20 per :cent amyl nitrate, 60 per cent of 45-octane straight-run gasoline, 18 per cent SAE SO-lubricating oil, and 2 per cent oleic acid was blended. This fuel was charged to a glow type test motor, and the test motor developed a top speed under propeller load of approximately 16,000 R. P. M., which was more than 3,000 R. P. M. higher than previously obtained with any commercial fuel. This mixture started easily with either a hot or cold motor, whereas the previous commercial fuels had difficulty in starting with a cold motor unless primers, such as ether, were used, and the latter is not desirable due to the fire hazard. Further, this fuel of my invention caused no seizing even at top speeds, whereas seizing has been a serious problem with commercial fuels heretofore used. In addition, almost a two-fold increase in operating time for the motor was obtained over present commercial fuels, which is also of considerable advantage.

A similar fuel containing, by volume, 40 percent amyl nitrate, 20 percent of Pennsylvania bright stock, and 40 percent of a full range alkylate gasoline was found to give similar excellent results in the glow-plug test engine.

Equally good results are obtained with other fuels of this invention. For example, a mixture, by volume, of 20 percent of n-propyl nitrate, 60 percent of 50'octane gasoline containing about 65 percent of paratfinic hydrocarbons, 18 per cent of SAE SO-lubricating oil, and 2 percent of glycerol, when tested in a glow-plug type test engine, produces a top speed, under propeller load, of approximately 15,000 R. P. M. Comparable results are obtained from a similar fuel containing n-butyl nitrate.

Other excellent fuels can be readily prepared within the scope of my invention, which'is covered by the following claim.

I claim:

A motor fuel suitable for use in glow-plug engines, consisting essentially of, by volume, between about 20 and 40 percent of amyl nitrate; 15 to percent of a heavy hydrocarbon lubricating oil having an SAE viscosity of at least 2 to 5 percent of glycerol, and the balance being not over 40 percent of a gasoline containing at least about percent by volume of paraflinic hydrocarbons, said gasoline having an octane number in the range of about 40 to about 60.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Model Motor Manual, Air Age 1110., 551-5th Ave,

New York 17, N. Y., 1947, page so, 

